Automatic pet doors actuated by a magnet worn by a pet have numerous advantages over other types of automatic pet doors. These advantages include preventing unauthorized pets from opening the pet door, allowing the authorized pets to open the pet door without having to force it open, being relatively secure against burglars, reliably weatherproof and inexpensive to provide and install.
However, automatic pet doors actuated by a magnet worn by a pet of the prior art have a disadvantage, namely, they may react to the Earth's ambient magnetic field rather than the magnet worn by a pet, causing unintended openings. Such unintended openings happen most frequently in the automatic pet doors installed in hinged entrance doors to a residence. When a pet owner opens the entrance door, the magnetic detector adapted to react to the specific rate of motion of the magnet worn by the pet moves in an ark through the Earth's magnetic field. The magnetic detector frequently cannot distinguish between the motion of the magnet worn by the pet and the motion of the door, thus causing the pet door to open. This causes annoyance to pet owners and is undesirable.
Unintended openings may also be caused by rattling of the entrance door due to a storm, earthquake and the like, or even by a pet that is not allowed to go out scratching and attacking the pet door. Another undesirable situation is when the pet owner and the pet wearing a magnet reach an entrance door together, the pet door may open at the same time as the entrance door and the pet owner may accidentally drag the pet that is half way through the pet door.
Therefore, there is a need for an automatic pet door actuated by a magnet worn by a pet that prevents unintended openings caused by the Earth's ambient magnetic field.